Posted by Adam Quinan on February 12, 2013 at 14:59:11 user Adam.
In Reply to: Re: Peggy sometimes Margaret (was "Nancy based on Lenin?") posted by Peter Ceresole on February 12, 2013 at 13:54:26:
Jack is certainly a common nickname for people named John. I wouldn't say they are interchangeable though. I think people either go with John or Jack but don't usually switch between them, unless Jack is formally asked for his proper name.
Though if you wanted to look at the Latin roots, you might think that Jack should be a nickname for James (Latin Jacobus).